1. Field of the Invention
The present invention relates to a display device, specifically, to an active matrix display device.
2. Description of the Related Art
Rapid development has been made lately in a technique of manufacturing an electronic device such as a thin film transistor (TFT), for example, in which a thin film semiconductor is formed on an inexpensive glass substrate. This is due to an increasing demand for an active matrix liquid crystal panel.
The active matrix liquid crystal panel has a pixel portion in which several hundred thousands to several million TFTs are arranged in a matrix-like manner, and displays an image by controlling electric charges flowing in and out of pixel electrodes connected to each of the TFTs by means of a switching function of the TFTs.
Conventionally, thin film transistors arranged in the pixel portion are fabricated using amorphous silicon that is formed on a glass substrate.
However, in recent years, it has been found that a thin film transistor could be formed from a polycrystalline silicon film while using quartz as a substrate. In this case, peripheral driver circuits are integrated with the pixel portion so that both the circuits and the pixel portion are formed on the quartz substrate.
A technique is also known in which a thin film transistor is fabricated from a crystalline silicon film formed on a glass substrate by using laser annealing or other technologies.
However in addition to large active matrix liquid crystal panels used as display devices in personal computers, smaller ones used in front projectors, rear projectors, and Head Mounted Displays (HMD) have recently emerged. Smaller is better since smaller active matrix liquid crystal panels can be used for increasingly smaller electronic devices. Recently, a panel the size of about 0.7 inches, diagonally, is being mass produced.
Referring to FIG. 17, the structure of a conventional active matrix liquid crystal panel is shown schematically. In FIG. 17, reference numeral 11000 denotes a liquid crystal panel, 11100, a source driver, 11200, a gate driver, 11300, a pixel portion, and 11400, an FPC terminal. The FPC terminal is a terminal for inputting video data, a clock signal, a power supply, etc. to the liquid crystal panel. When the lateral length of the pixel portion is given as W and the longitudinal length thereof as H, W/H is generally 4/3 or 16/9.
Due to the recent demand for miniaturization, however, it is no longer possible to construct such smaller display devices in accordance with the circuit layout shown in FIG. 17. For instance, in some liquid crystal panels, the size of the substrate has to be reduced in the longitudinal direction of the gate driver. When this occurs, there is no longer enough area for the source driver to occupy. In other words, the number of elements constituting the source driver is greater as compared with the gate driver, and accordingly the source driver occupies a larger area. The conventional circuit layout can not deal with miniaturization because the source driver occupies too large of an area.